netdev - Re: [PATCH net-next] net: dsa: b53: Slightly optimize b53_arl

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Date:   Thu, 20 Apr 2023 17:40:45 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Andrew Lunn <andrew@...n.ch>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: b53: Slightly optimize b53_arl_read()



On 4/20/2023 1:44 PM, Christophe JAILLET wrote:
> When the 'free_bins' bitmap is cleared, it is better to use its full
> maximum size instead of only the needed size.
> This lets the compiler optimize it because the size is now known at compile
> time. B53_ARLTBL_MAX_BIN_ENTRIES is small (i.e. currently 4), so a call to
> memset() is saved.
> 
> Also, as 'free_bins' is local to the function, the non-atomic __set_bit()
> can also safely be used here.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>   drivers/net/dsa/b53/b53_common.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
> index 3464ce5e7470..8c55fe0e0747 100644
> --- a/drivers/net/dsa/b53/b53_common.c
> +++ b/drivers/net/dsa/b53/b53_common.c
> @@ -1627,7 +1627,7 @@ static int b53_arl_read(struct b53_device *dev, u64 mac,
>   	if (ret)
>   		return ret;
>   
> -	bitmap_zero(free_bins, dev->num_arl_bins);
> +	bitmap_zero(free_bins, B53_ARLTBL_MAX_BIN_ENTRIES);

That one I am not a big fan, as the number of ARL bins is a function of 
the switch model, and this illustrates it well.

>   
>   	/* Read the bins */
>   	for (i = 0; i < dev->num_arl_bins; i++) {
> @@ -1641,7 +1641,7 @@ static int b53_arl_read(struct b53_device *dev, u64 mac,
>   		b53_arl_to_entry(ent, mac_vid, fwd_entry);
>   
>   		if (!(fwd_entry & ARLTBL_VALID)) {
> -			set_bit(i, free_bins);
> +			__set_bit(i, free_bins);

I would be keen on taking that hunk but keep the other as-is. Does that 
work for you?
--
Florian